error_handling.praia

// ── try/catch: catching explicit throw ──
try {
    print("before throw")
    throw "something went wrong"
    print("this never runs")
} catch (err) {
    print("caught:", err)
}

// ── try/catch: catching runtime errors ──
try {
    let x = 1 / 0
} catch (err) {
    print("caught runtime error:", err)
}

try {
    let arr = [1, 2, 3]
    print(arr[99])
} catch (err) {
    print("caught:", err)
}

// ── throw any value ──
try {
    throw {code: 404, message: "not found"}
} catch (err) {
    print("error code:", err.code, "message:", err.message)
}

// ── nested try/catch ──
try {
    try {
        throw "inner error"
    } catch (e) {
        print("inner catch:", e)
        throw "re-thrown from inner"
    }
} catch (e) {
    print("outer catch:", e)
}

// ── try/catch with functions ──
func divide(a, b) {
    ensure (b != 0) else {
        throw "division by zero"
    }
    return a / b
}

try {
    print("10 / 3 =", divide(10, 3))
    print("10 / 0 =", divide(10, 0))
} catch (err) {
    print("caught:", err)
}

// ── ensure: early exit guard ──
func greet(name) {
    ensure (name) else {
        print("no name provided")
        return
    }
    print("hello %{name}!")
}

greet("Ada")
greet(nil)
greet("Bob")

// ── ensure: validate input ──
func processAge(age) {
    ensure (type(age) == "number") else {
        throw "age must be a number"
    }
    ensure (age >= 0 && age <= 150) else {
        throw "age out of range: %{age}"
    }
    print("valid age: %{age}")
}

try { processAge(25) } catch (e) { print(e) }
try { processAge(-5) } catch (e) { print(e) }
try { processAge("old") } catch (e) { print(e) }

// ── safe file reading with try/catch ──
func readFile(path) {
    try {
        return sys.read(path)
    } catch (err) {
        return nil
    }
}

let content = readFile("/tmp/nonexistent_file_12345.txt")
ensure (content) else {
    print("file not found, using default")
    content = "default value"
}
print("content:", content)